Assertion (A): For a gas reacting on a solid catalyst, the rate increases linearly with gas pressure at all pressures. Reason (R): The number of active sites on the catalyst surface is limited and they become saturated at high pressure.

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true

Answer: D

At low pressure the rate is proportional to coverage and hence to pressure, but at high pressure the surface is saturated and the rate becomes independent of pressure (zero order). So A is false, while R is true.

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